README.md

Chisel examples

This directory contains a variety of Chisel¹ code examples and their respective test benches. A selection of these examples has been meticulously chosen from the chisel-tutorial² GitHub repository and subsequently adapted for an analysis of each testing framework characteristics. The primary objective of these modifications is to highlight certain characteristics of Chisel representations that might remain obscured while using the available testing frameworks.

Specifically, the list of selected examples is presented below:

• Adder: A simple N-bit adder circuit, that uses the scala Array class to wrap the FullAdder modules and chisel Vec/Bundle³ to group together signals needed for the internal carry, sum and IO interface.
• DetectTwoOnes: A simple finite state machine that uses ChiselEnum⁴ to represent the states.
• Parity: A simple circuit that uses an Enum⁵ (chisel) to represent the states instead of ChiselEnum.
• Functionality: A simple circuit that uses different ways to assign values to outputs:
  • Direct output assignment from pure boolean expressions
  • Wrapping the boolean expressions into a def function
  • Wrapping the boolean expression into a val
  • Using a scala object.
  • Using a scala class.
• Memory: A simple module that wraps the Mem⁶ (chisel) module to implement a simple read/write memory.
• Router: This is the most complex example. It implements a simple router which characteristics are wrapped into objects and classes. It is composed by:
  • A top Router module class that instantiates submodules and connect wires together.
  • A RouterIO class that defines the IO interface of the router.
  • A Packet class that defines the structure of a packet that goes through the router.
  • A WriteCmd and a ReadCmd classes that define the structure of the commands that the router receives.
  • A Router object that defines constants that specify the characteristics of the router.
  • A Mem instance to define the routing table.

Each example aims to illustrate the representation of a particular aspect supported by Chisel in the testing frameworks. It also shows how such aspect relates to the Chisel source code. Sources and tests are located in the src/main and src/chiseltest subdirectories, respectively.

Examples summary

Example	Target
Adder	Explore the representation of chisel Bundle/Vec and scala Array in testing frameworks.
FSM and Parity	Understand how ChiselEnum and Enum are depicted in testing frameworks.
Functionality	Analyze the impact of various assign values methods on output representation in testing frameworks.
Memory	Explore the representation of chisel Mem in testing frameworks.
Router	Examine the impact of various strategies for representing constants and circuit components in testing frameworks.

Note: The examples are used to perform the analysis of the testing frameworks. Results are reported in the results directory.

References

Footnotes

1. Chisel, an open-source hardware description language (Constructing Hardware in a Scala Embedded Language). ↩

2. A collection of Chisel tutorials and examples. ↩

3. Bundles and Vecs | Chisel. en. ↩

4. Enumerations | Chisel. en. ↩

5. chisel3.util.Enum documentation en. ↩

6. Memories | Chisel. en. ↩